Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752819AbdHKKuZ (ORCPT ); Fri, 11 Aug 2017 06:50:25 -0400 Received: from bombadil.infradead.org ([65.50.211.133]:37948 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752406AbdHKKuY (ORCPT ); Fri, 11 Aug 2017 06:50:24 -0400 Date: Fri, 11 Aug 2017 12:50:15 +0200 From: Peter Zijlstra To: Nadav Amit Cc: linux-mm@kvack.org, nadav.amit@gmail.com, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Minchan Kim , Sergey Senozhatsky , Andy Lutomirski Subject: Re: [PATCH v6 3/7] Revert "mm: numa: defer TLB flush for THP migration as long as possible" Message-ID: <20170811105015.4njdpy3il76g5uuk@hirez.programming.kicks-ass.net> References: <20170802000818.4760-1-namit@vmware.com> <20170802000818.4760-4-namit@vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170802000818.4760-4-namit@vmware.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 663 Lines: 13 On Tue, Aug 01, 2017 at 05:08:14PM -0700, Nadav Amit wrote: > While deferring TLB flushes is a good practice, the reverted patch > caused pending TLB flushes to be checked while the page-table lock is > not taken. As a result, in architectures with weak memory model (PPC), > Linux may miss a memory-barrier, miss the fact TLB flushes are pending, > and cause (in theory) a memory corruption. > > Since the alternative of using smp_mb__after_unlock_lock() was > considered a bit open-coded, and the performance impact is expected to > be small, the previous patch is reverted. FWIW this Changelog sucks arse; you completely fail to explain the broken ordering.